Conventionally, a frictional engagement device, such as a clutch for an automatic transmission of an automobile, is provided with a friction member formed of a cored bar made of ferric metal in a shape of a plate, and a friction material, such as cellulose fiber, adhered to the cored bar. The friction material is generally called a paper friction material, which is obtained by impregnating an organic fiber material in a form of paper with a solution prepared by dissolving a resin for a friction material into an organic solvent, drying and heat hardening the resultant substance. A friction material formed of carbon fiber has been also known where carbon fiber is used for a purpose of reducing size and weight (see, for example, JP 11-5850A, paragraphs 0019-0020).
The friction members with the friction material adhered thereto are laminated alternately with separator plates as coupling members, to thereby form a multiple disc clutch, which is disposed as a driving force transmission member in a frictional engagement device. In the frictional engagement device, driving force to wheels is transmitted from an engine by bringing the friction member into contact with the separator plate by pressure, and driving force to the wheel is cut off by spacing the friction member apart from the separator plate.
In the friction member to be used in the conventional frictional engagement device, a part forming the cored bar is made of a metallic plate, and there is a problem of friction members becoming heavier. Therefore, reduction in weight has been desired. In order to reduce the weight of the friction member, there can be mentioned a technique in which an entire friction member including the cored bar is formed of baked carbon fiber. However, this technique has a problem in that impact resistance is lowered, even though the weight reduction of the friction member is attained.
A production of such a friction member generally requires baking carbon by a high-temperature baking in a high temperature range of 1000-2000° C.; impregnating a space formed by vaporization with a resin liquid; baking again; and repeating these steps. Therefore, such a friction member has a problem in that the production is time-consuming and expensive.
In addition, a recent frictional engagement device, such as a clutch for an automatic transmission, attains a high level of performance and becomes highly functional. In accordance with this development, improvement in a friction coefficient (frictional properties) of the friction member has been demanded.